If you want something to a power use the little up arrow, upper case 6. For example x^3 is x cubed.
a)
1.67 * 10^-27 * 4.00*10^6
=(1.67*4)* 10^-21
= 6.68 * 10^-21 kg m/s
all to three significant figures since 4.00 and 1.67 are three figures